The present invention relates generally to a device for conditioning an aerosol such as that resulting from the nebulization of a liquid sample, and more particularly to a device for removing large droplets from an aerosol stream so as to enable improved stability of analytical signals derived from the aerosol.
Since the early days of flame emission spectrometry, it has been realized that a spray chamber placed between the nebulizer and burner could function as a droplet separator and a flow buffer to remove large droplets from the sample aerosol and thereby improve the stability of analytical signals derived from the aerosol. Usually such spray chambers were made from available laboratory glassware. Yet, even these relative crude early designs were so effective that similar spray chamber units are still commonly employed today in atomic absorption and flame emission instrumentation. These spray chambers were later scaled down, somewhat modified and adapted to use in inductively coupled plasma spectrometry.
In all of these spray chambers, the removal of large droplets is inevitably accompanied by a reduction in the transport efficiency of aerosol and analyte to the subsequent atomization/excitation source. For example, measurements carried out on a typical inductively coupled plasma (ICP) nebulizer/spray chamber system reveal that more than 98% of the aerosol is lost to waste. As a result, the transport efficiency of a typical ICP system is only in the range of about 0.5%-2%. Also, fine droplets are suspended and circulate inside the spray chamber, resulting in relatively long wash-out times. For a typical system, it usually takes several minutes to change a sample. Such recognized low transport efficiencies and large memory effects have existed in atomic spectrometry for nearly a half century and they remain among the weak links in the field.
Continuing efforts have been made to improve nebulizer/spray chamber systems. Single- and double-barrel Scott-type spray chambers, cyclone configurations, baffles, and gravitational sedimentation chambers have been used in inductively coupled plasma emission spectrometry (ICP-AES). Other techniques have also been explored to circumvent conventional nebulizer-spray chamber systems. For example, jet-impact and direct-injection nebulization have been used with inductively coupled plasma emission and mass spectrometry. Fundamental investigations into aerosol characterization have offered some insight into the performance of aerosol chambers and its dependence on centrifugal force, evaporation, gravitation, impaction, and turbulence. Nevertheless, there still exists a need for improved spray chambers providing increased throughput and stability to analytical signals derived from sample aerosols. The present invention addresses this need.